Physicists are warning that the universe may end in a "big crunch", with some suggesting this could occur in 20 billion years, although the exact timeframe is uncertain. The prediction is based on new data related to dark energy, which may cause the universe's expansion to reverse. The timing of the potential "big crunch" is reported differently, with one outlet mentioning 33 billion years, but the general consensus is that the universe may ultimately collapse in on itself.